Q: Is it true that your metabolic rate actually decreases if you workout too long??

A: That is correct. Slower metabolism despite lots of weightlifting and/or cardio is another symptom of overtraining. It is actually very common among people who are so into exercising that they fall into 'more is always better' trap. How much one can train before overtraining can vary quite a bit from person to person, so I try to give guidelines that will work for an average man or woman. If you look at my sample routines, most of them are marked as 'low', 'medium', or 'high' volume -- that should give you an idea of the amounts of weights work that an average person should do in a week. A rule of thumb is to do between 2 and 5 hours of weights per week.